A normal blood pressure reading measures 120/80 millimeters of mercury, as stated by WebMD. Blood pressure is a measure of the amount of force the blood has on arteries, with higher readings being more dangerous.
The first number of the measurement is called the systolic measurement, states WebMD. This number indicates the force blood has on an individual's arteries when the heart beats. The second number is called the diastolic and represents the pressure of an individual's blood when at rest. One is said to have borderline high blood pressure if it's measured above 120/80 but lower than 140/90. Having blood pressure at 140/90 or above is called hypertension, which puts individuals at risk to develop heart disease.